Failed update: ispconfig and phpmyadmin unreachable, apache is fine

I ran the update script from 3.0.15. to 3.0.16 on two servers. One updated just fine. One the second, I got a crashed apache and ispconfig. I restarted apache and my websites are live, but I can't re-run the update (says it's already at 3.0.16.)

Now ispconfig will start, but I can't log in. password is wrong (i've tried the admin/admin log in as well as my usual login).

And phpmyadmin won't load. I get a 403 forbidden error.

I tried downloading the update and doing a manual install, but I get the following error:
Fatal error: Cannot use string offset as an array in /tmp/ispconfig3_install/install/update.php on line 199

I checked the server I thought was fine: While I'm able to log into ISPConfig on that one, I still can't get to phpmyadmin. So this is not an issue with just a single server. Several other people have the same or similar issue: